Blowing ignition a fuse

I believe you mean a 40 amp fuse? Wow! that's a dead short somewhere on a large wire. Could be difficult, or hopefully easy to find. There's always the smoke test option: Solder a jumper wire across the top of the fuse, making the circuit essentially un-fused and look for the smoke. Not the best method, but quick. Warning: if you do this, depending on where the short is, you could melt down the wire harness or possibly start a fire. Try this at your own risk! IT'S A "LAST RESORT" THING, WHEN YOU'VE TRIED EVERYTHING ELSE AND FAILED! Good luck.